U.S. patent number 4,241,406 [Application Number 05/971,967] was granted by the patent office on 1980-12-23 for system and method for analyzing operation of an ink jet head.
This patent grant is currently assigned to International Business Machines Corporation. Invention is credited to Donald L. Janeway, Eugene T. Kennedy.
United States Patent |
4,241,406 |
Kennedy , et al. |
December 23, 1980 |
System and method for analyzing operation of an ink jet head
Abstract
A system and method are disclosed for analyzing operation of an
ink jet head. Initiation of start-up is sensed, as is the pressure
build-up in the ink jet head as ink is supplied thereto. The time
lapse between initiation of start-up and the commencement of
pressure build-up is determined, as is the time required for the
pressure within the ink jet head to build to an operational level,
and outputs indicative thereof are utilized for determination of
fault occurrence and indication of faults or initiation of fault
correction in response thereto. The system includes a pair of
counters controlled by start-up initiation and the outputs from a
pair of comparators which receive predetermined reference signals
and signals indicative of pressure build-up at the ink jet head,
with the outputs from the counters being coupled to a microcomputer
for determination of faults.
Inventors: |
Kennedy; Eugene T. (Longmont,
CO), Janeway; Donald L. (Broomfield, CO) |
Assignee: |
International Business Machines
Corporation (Armonk, NY)
|
Family
ID: |
25518995 |
Appl.
No.: |
05/971,967 |
Filed: |
December 21, 1978 |
Current U.S.
Class: |
346/33R; 347/5;
702/185; 702/138 |
Current CPC
Class: |
B41J
2/1707 (20130101) |
Current International
Class: |
B41J
2/17 (20060101); G01D 015/18 () |
Field of
Search: |
;364/500,518,519,523,571
;346/14R,75 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wise; Edward J.
Attorney, Agent or Firm: O'Rourke & Harris
Claims
What is claimed is:
1. A system for analyzing operation of an ink jet head from which
ink is ejected due to pressure within said head, said system
comprising:
sensing means for sensing the pressure characteristic in the ink
jet head during a predetermined pressure change period; and
determining means connected with said sensing means for determining
pressure build-up within said ink jet head to thereby detect faults
in performance of said ink jet head based upon said pressure
characteristics sensed by said sensing means.
2. The system of claim 1 wherein said sensing means includes a
pressure responsive transducer at said ink jet head for sensing the
pressure thereat and providing an electrical output signal
proportional thereto.
3. The system of claim 2 wherein said pressure responsive
transducer is a piezoelectric crystal.
4. The system of claim 1 wherein said determining means includes
time determining means for determining the amount of time necessary
for pressure in said ink jet head to build to a predetermined
pressure level during start-up.
5. The system of claim 4 wherein said time determining means
includes a counter actuated at the initiation of start-up and a
comparator for stopping the count on said counter when said
pressure in said ink jet head reaches said predetermined pressure
level.
6. The system of claim 5 wherein said counter is connected with a
gate receiving a clock input and an indication of initiation
start-up whereby said counter counts at the frequency of said clock
when said clock is actuated at initiation of start-up.
7. The system of claim 4 wherein said time determining means
includes means for determining the amount of time necessary for
pressure in said ink jet head to build to at least two different
predetermined pressure levels during start-up.
8. The system of claim 7 wherein said time determining means
includes first and second counters and first and second comparators
connected with said sensing means, with said first counter being
actuated to start counting at the initiation of start-up and
connected to said first comparator to stop counting when the
pressure in said ink jet head reaches a first of said predetermined
different pressure levels, and with said second counter being
connected with said first comparator to start counting when said
pressure in said ink jet head reaches said first predetermined
pressure level and connected with said second comparator to stop
counting when said pressure in said ink jet head reaches the second
of said predetermined different pressure levels.
9. The system of claim 8 wherein said first and second counters are
connected with said first and second gates, respectively, both of
which receive a clock input and with said first and second gates
also receiving an indication of initiation of start-up and the
output from the first comparator, respectively, whereby each
counter is caused to count at the frequency of said clock until
said count is terminated.
10. The system of claim 1 wherein said system includes means for
causing initiation of a recovery procedure based on a fault
determined by said determining means.
11. The system of claim 10 wherein said means for causing
initiation of said recovery procedure includes a microcomputer.
12. The system of claim 11 wherein said microcomputer includes
memory means for receiving indications of faults from said
detecting means.
13. The system of claim 12 wherein said microcomputer includes a
microprocessor.
14. The system of claim 13 wherein said system includes indicating
means for indicating a need for valve maintainence, and wherein
said microprocessor controls activation of said indicating means in
response to an output from said memory means indicative of valve
fault.
15. The system of claim 14 wherein said system includes storing
means for storing valve pick number and delay, and wherein said
microprocessor controls coupling of a signal to said storage means
when said indicating means is actuated.
16. The system of claim 13 wherein said microprocessor updates the
frequency distribution of start time in response to data from said
memory means.
17. The system of claim 13 wherein said microprocessor updates the
frequency distribution of rise time in response to data from said
memory means.
18. The system of claim 13 wherein said microprocessor causes
initiation of printing by said ink jet head when said memory means
indicates that the rise time of pressure on said ink jet head is
less than a predetermined value indicative of the maximum
permissible rise time.
19. The system of claim 13 wherein said microprocessor causes
initiation of printing by said ink jet head after a predetermined
delay when said memory means indicates that the rise time of
pressure on said ink jet head is less than a first predetermined
value indicative of the maximum permissible rise time and is
greater than, or equal to, a second predetermined value indicative
of air in the ink in said ink jet head.
20. A system for analyzing operation of an ink jet head, said
system comprising:
a piezoelectric crystal for sensing the pressure at an ink jet head
and providing an electrical output signal proportional to the
pressure sensed;
a first comparator for comparing the pressure sensed by said
piezoelectric crystal and a first reference level, said first
comparator providing an output when said pressure sensed by said
piezoelectric crystal exceeds said first reference level;
a second comparator for comparing the pressure sensed by said
piezoelectric crystal and a second reference level, said second
comparator providing an output when said pressure sensed by said
piezoelectric crystal exceeds said second reference level;
a first counter connected with said first comparator for counting
from initiation of start-up until said first pressure level is
exceeded at said ink jet head;
a second counter connected with said first and second comparators
for counting from the time that said first pressure level is
exceeded until said second reference level exceeds at said ink jet
head; and
a microcomputer connected with said first and second counters for
initiating at least one of indication and correction when said
count on said counters indicates a fault in operation of said ink
jet head.
21. The system of claim 20 wherein said microcomputer includes a
delay register and a rise time register for receiving and
individually storing the counts on said counters.
22. The system of claim 21 wherein said registers are connected
with said counters through logic gates.
23. The system of claim 21 wherein said microcomputer includes a
microprocessor connected with said registers.
24. The system of claim 23 wherein said system includes light means
for indicating a need for valve maintainence, and wherein said
microprocessor controls energization of said light means in
response to data from said delay register is indicative of valve
fault.
25. The system of claim 24 wherein said system includes storing
means for storing valve pick number and delay, and wherein said
microprocessor controls coupling of a signal to said storage means
when said light means is energized.
26. The system of claim 23 wherein said microprocessor updates the
frequency distribution of start time in response to data from said
rise time register.
27. The system of claim 23 wherein said microprocessor updates the
frequency distribution of rise time in response to data from said
rise time register.
28. The system of claim 23 wherein said microprocessor causes
initiation of printing by said ink jet head when said rise time
register indicates that the rise time of pressure in said ink jet
head is less than a predetermined value indicative of the maximum
permissible rise time.
29. The system of claim 23 wherein said microprocessor causes
initiation of printing by said ink jet head after a predetermined
delay when said rise time register indicates that the rise time of
pressure in said ink jet head is less than a first predetermined
value indicative of the maximum permissible rise time and is
greater than, or equal to, a second predetermined value indicative
of air in the ink in said ink jet head.
30. A system for analyzing operation of a device having a material
flow initiating unit and a pressure drive for expelling material
from said device, said system comprising:
sensing means connected with said material flow initiating unit for
sensing initiation of material flow and providing an output
indicative thereof;
transducer means for vibrating said flow during normal operation of
said transducer means and also sensing pressure build-up in said
device following initiation of material flow and providing an
output indicative of said pressure build-up; and
determining means connected with said sensing means and said
transducer means to receive said outputs therefrom and responsive
thereto determining the time lapse between initiation of material
flow and pressure build-up.
31. The system of claim 30 wherein said sensing means produces
electrical output signals indicative of initiation of material flow
and pressure build-up, and wherein said determining means includes
electrical means for receiving said outputs and determining
therefrom said time lapse.
32. The system of claim 31 wherein said determining means includes
counter means.
33. The system of claim 30 wherein said transducer means includes a
piezoelectric crystal for providing an electrical output
proportional to pressure sensed in said device.
34. The system of claim 30 wherein said determining means includes
comparator means for comparing said indicated pressure with a
reference pressure.
35. The system of claim 34 wherein said reference pressure is
chosen so that initial build-up of pressure is effectively
sensed.
36. The system of claim 34 wherein said reference pressure is
chosen so that an operational pressure is effectively sensed.
37. The system of claim 34 wherein a plurality of reference
pressures are utilized for comparison so that both initial build-up
of pressure and achievement of an operational pressure are
effectively sensed.
38. The system of claim 30 wherein said system includes utilization
means for receiving said determined time lapse from said
determining means and responsive thereto indicating faults in
operation of said device.
39. The system of claim 38 wherein said utilization means includes
a microcomputer.
40. The system of claim 30 wherein the material flow monitored is
ink supplied to an ink jet head, wherein said material flow
initiating device includes a valve connected with said ink jet head
and controlled by a valve control unit, and wherein said sensing
means is connected with said valve control unit to sense initiation
of ink flow.
41. The system of claim 40 wherein said valve control unit includes
electrical means providing an electrical output signal indicative
of initiation of ink flow to said sensing means, wherein said
transducer means is in said ink jet head and produces an electrical
output signal indicative of pressure build-up in said ink jet head,
and wherein said determining means includes counter means for
receiving said electrical output signals and responsive thereto
determining said time lapse.
42. A system for analyzing operation of an ink jet head receiving
ink from an ink supply through a valve controlled by a valve
control unit so that ink received at said ink jet head is ejected
under pressure therefrom, said system comprising:
first sensing means for sensing actuation of said valve control
unit to open said valve and providing an output indicative
thereof;
second sensing means for sensing pressure build-up in said ink jet
head and producing an output indicative thereof; and
time lapse determining means for receiving said output from said
first and second sensing means and responsive thereto producing an
output indicative of the time lapse between said actuation of said
valve and said pressure build-up in said ink jet head.
43. The system of claim 42 wherein said first sensing means senses
actuation of said valve control unit and responsive thereto
provides an electrical output signal, and wherein said second
sensing means includes a pressure responsive transducer at said ink
jet head, said transducer providing an electrical output signal
proportional to pressure sensed in said ink jet head.
44. The system of claim 43 wherein said time lapse determining
means includes counter means actuated under the control of said
electrical output signal from said first and second sensing means
to produce a count indicative of said time lapse.
45. The system of claim 44 wherein said time lapse determining
means includes a gate connected to receive a clock input at a
predetermined frequency and said electrical output signal from said
first sensing means with said gate providing an output to said
counter means for causing said counter means to count at said clock
frequency, and a comparator for receiving a reference signal input
at a predetermined level and said electrical signal output from
said transducer with said comparator providing an output to said
counter means to cause said count thereon to be terminated when
said electrical signal output from said transducer exceeds said
reference signal coupled to said comparator.
46. The system of claim 45 wherein said counter means of said time
lapse determining means includes first and second counters with
said gate and comparator being connected with said first counter,
and wherein said time lapse determining means also includes a
second gate connected to receive said clock input and output from
said comparator with the output from said second gate being coupled
to said second counter to cause said second counter to count said
clock frequency, and a second comparator connected to receive a
second reference input signal at a predetermined level different
from that of said first predetermined level and the electrical
output signal from said transducer with the output from said second
comparator being coupled to said second counter to cause said count
thereon to be terminated when said electrical output signal from
said transducer exceeds said second reference signal coupled to
said second comparator.
47. The system of claim 42 wherein said system includes utilization
means connected with said time lapse determining means for
controlling operation of said ink jet head.
48. The system of claim 42 wherein said utilization means includes
a microcomputer.
49. The system of claim 48 wherein said microcomputer includes
memory means connected with said time lapse determining means for
storing said determined time lapse.
50. The system of claim 48 wherein said memory means is connected
with said time lapse determining means through a data bus and a
logic gate controlled by an address decode unit.
51. A system for analyzing operation of a material inking unit
having ink flow from an ink supply to an ink jet head through a
valve controlled by an electrical valve control unit with the ink
being ejected under pressure from the ink jet head, said system
comprising:
a first gate connected to receive a clock input at a predetermined
frequency and the electrical output signal from said electrical
valve control unit indicative of initiation of inking in said
inking unit, said first gate providing an output at said clock
frequency upon receipt of said electrical output signal indicative
of initiation of inking;
a delay counter connected to said first gate to receive said output
therefrom to cause said delay counter to count at said clock
frequency;
a piezoelectrical crystal at said ink jet head to sense the
pressure thereat and providing an output signal indicative
thereof;
a first comparator connected to receive a reference input signal at
a predetermined level and said output signal from said
piezoelectric crystal, said first comparator providing an output to
said delay counter to terminate the count thereat when said output
signal from piezoelectric crystal exceeds the level of said first
reference input signal;
a second gate connected to receive said clock input and the output
from said first comparator, said second gate providing an output at
said clock frequency upon receipt of said output from said first
comparator;
a rise time counter connected to said second gate to receive said
output therefrom to cause said rise time counter to count at said
clock frequency;
a second comparator connect to receive a reference input signal at
a predetermined level greater than said first predetermined level
and said output signal from said piezoelectric crystal, said second
comparator providing an output to said rise time counter to
terminate the count thereat when said output signal from said
piezoelectric crystal exceeds the level of said second reference
input signal;
a microcomputer having a delay register and a rise time
register;
coupling means including first and second logic gates connected
with said delay counter and said rise time counter, respectively,
with said first and second gates being connected with said delay
register and said rise time register, respectively, through a data
bus; and
address decode means connected with said microcomputer and said
first and second gates for controlling passage of the counts on
said counters to said registers of said microcomputer.
52. The system of claim 51 wherein said system includes crystal
drive means and switching means for switching said piezoelectric
crystal between said crystal drive means and said first and second
comparators depending upon the mode of operation then desired.
53. A method for analyzing operation of an ink jet head from which
ink is ejected due to pressure within said head, said method
comprising:
sensing the pressure characteristic in an ink jet head during a
predetermined pressure change period; and
determining pressure build-up within said ink jet head to thereby
detect faults in performance of said ink jet head based upon said
sensed pressure characteristic.
54. The method of claim 53 including providing an electrical output
signal proportional to said sensed pressure characteristic and
utilizing said electrical output signal to detect said faults in
the performance of said ink jet head.
55. The method of claim 53 including sensing indication of
start-up, sensing of pressure build-up in said ink jet head to a
predetermined pressure level, and detecting therefrom said faults
in performance of said ink jet head.
56. The method of claim 55 including providing a count between
initiation of start-up and pressure build-up in said ink jet head
to a predetermined pressure level to determine the time lapse
therebetween.
57. The method of claim 56 including comparing said pressure in
said ink jet head with a predetermined pressure level and utilizing
the result thereof to determine said count.
58. The method of claim 53 including also determining the time
lapse between said predetermined pressure level and a second
predetermined pressure level in said ink jet head and utilizing the
same in conjunction with said time lapse between initiation of
start-up and said predetermined pressure level to detect said
faults in performance of said ink jet head.
59. The method of claim 53 including utilizing said detected faults
to initiate correction of said detected faults.
60. The method of claim 59 including storing said detected faults
to facilitate correction of said detected faults.
61. A method for monitoring operation of a device having a material
flow initiating unit and a pressure drive for expelling material
from said device, said method comprising:
sensing initiation of material flow in said device;
utilizing a transducer to vibrate the flow during normal operation
and utilizing the same transducer to sense pressure build-up in
said device following initiation of material flow; and
determining the time lapse between sensed initiation of material
flow and pressure build-up as sensed by the transducer for
monitoring operation of said device.
62. The method of claim 61 including providing electrical output
signals indicative of sensed initiation of material flow and
pressure build-up and utilizing said electrical output signals to
determine said time lapse.
63. The method of claim 62 including utilizing said electrical
output signals to provide a count indicative of said time
lapse.
64. The method of claim 61 including sensing pressure build-up at
different operational levels and utilizing the same in conjunction
with said sensed initiation of material flow to determine said time
lapse.
65. The method of claim 61 including utilization of said determined
time lapse to initiate correction of faults indicated by said time
lapse.
66. A method for analyzing operation of an ink jet head, said
method comprising:
sensing initiation of start-up of the ink jet head;
sensing pressure build-up in said ink jet head to a predetermined
level; and
determining the time lapse between said sensed initiation of
start-up and said pressure build-up for analyzing operation said
ink jet head.
67. The method of claim 66 wherein a count is commenced upon
initiation of start-up, and wherein said count is terminated when
said sensed pressure build-up exceeds said predetermined reference
level.
68. The method of claim 66 including utilizing said determined time
lapse to initiate correction of faults indicated by said time
lapse.
69. The method of claim 66 wherein said pressure build-up is sensed
at different predetermined levels, and utilizing said sensed
pressure build-ups and said sensed initiation of start-up for
analyzing operation of said ink jet head.
70. The method of claim 69 wherein a first count is commenced upon
sensing of initiation of start-up, wherein said first count is
terminated and a second count is commenced when said sensed
pressure build-up exceeds one of said predetermined reference
levels, and wherein said second count is terminated when said first
count exceeds the other of said predetermined reference levels.
71. The method of claim 70 including utilizing said counts to
initiate correction procedures if said counts are outside of
predetermined limits.
72. The method of claim 71 including utilizing said first count to
indicate a defect if said count is outside a predetermined range,
and utilizing said second count to correct defects if said count is
above a predetermined value.
73. The method of claim 72 wherein the initiation of start-up is
sensed by sensing initiation of actuation of a valve connected with
said ink jet head, wherein said first count is indicative of the
time lapse between initiation of valve actuation and the start of
pressure build-up in said ink jet head, and wherein said second
count is indicative of the time lapse between the start of pressure
build-up and achievement of operational pressure in said ink jet
head.
74. The method of claim 66 including storing of determined time
lapses indicative of start time and rise time.
75. The method of claim 74 including indicating a need for valve
maintainence when said stored start time is outside a predetermined
range.
76. The method of claim 75 including storing valve pick number and
delay information when a need for valve maintainence is
indicated.
77. The method of claim 74 including updating the frequency
distribution of stored start times in response to later sensed
start times.
78. The method of claim 74 including updating the frequency
distribution of stored rise times in response to late sensed rise
times.
79. The method of claim 74 including initiation of printing by said
ink jet head when the rise time of the pressure build-up in said
ink jet head is less than a predetermined value indicative of a
maximum permissible rise time.
80. The method of claim 74 including initiation of printing by said
ink jet head after a predetermined delay when the rise time of the
pressure build-up on said ink jet head is less than a first
predetermined value indicative of the maximum permissible rise time
and is greater than, or equal to, a second predetermined value
indicative of air in the ink in said ink jet head.
Description
This invention relates to an electronic monitoring system and
method, and, more particularly, relates to a system and method for
analyzing operation of an ink jet head.
BACKGROUND OF THE INVENTION
It is oftentimes desirable to maintain or analyze an apparatus to
enable correct operation and/or to provide an indication of faults
therein. Often, such an apparatus is self-correcting with the fault
indications being automatically utilized by the apparatus to make
the necessary corrections where possible.
Assurance of correct operation of the apparatus is particularly
important in many instances, including assurance of correct
operation of an ink jet head in a printing machine. In such a
machine, a valve is commonly opened to allow ink from a pressurized
source to pass to the ink jet head with a resulting pressure
build-up in the ink jet head. The speed of operation of the valve
and the time required for pressure build-up in the ink jet head
indicates the general condition of the valve and ink jet head. If
the operation of the valve is slow (or if the valve fails to open)
and/or if the pressure build-up within the jet head is slow, this
can indicate faulty operation and obviously can result in poor
printing quality.
While the prior art shows various start-up procedures for an ink
jet head (see, for example, U.S. Pat. Nos. 3,618,858 and
3,891,121), as well as control of ink concentration (see, for
example, U.S. Pat. Nos. 3,771,568, 3,930,258 and 3,828,172), there
is no known showing in the prior art of a system or method for
automated dynamic diagnosis of an ink jet head or recovery from a
fault therein.
SUMMARY OF THE INVENTION
This invention provides a system and method for analyzing operation
of a device and determining faults therein, as well as initiating
recovery procedures, where possible, when the presence of a fault
is determined. In particular, this invention provides a system and
method for analyzing operation of an ink jet head and determining
faults therein due to valve actuation and/or pressure build-up, as
well as initiating recovery procedures with respect thereto where
possible.
It is therefore an object of this invention to provide an
electronic system and method for monitoring operation of a
device.
It is another object of this invention to provide an electronic
system and method for initiating recovery procedures, where
possible, if a fault is determined in a device.
It is yet another object of this invention to provide a system and
method for analyzing operation of an ink jet head and utilizing the
same to determine faults therein.
It is still another object of this invention to provide a system
and method for analyzing operation of an ink jet head by
determining the time lapse between initiation of start-up and
pressure build-up to a predetermined level.
It is still another object of this invention to provide a system
and method for analyzing operation of an ink jet head by
determining the time lapse between initiation of start-up and
pressure build-up to two different predetermined levels.
It is yet another object of this invention to provide a system and
method for analyzing operation of an ink jet head by determining
pressure characteristics in the ink jet head and utilizing the same
to automatically initiate correction procedures if the pressure
characteristics indicate a fault in operation of the ink jet
head.
It is still another object of this invention to provide a system
for analyzing operation of an ink jet head that includes counters,
comparators and a microcomputer.
BRIEF DESCRIPTION OF THE DRAWINGS
The above-mentioned and other features and objects of this
invention and the manner of attaining them will become more
apparent and the invention itself will best be understood by
reference to the following description of embodiments of the
invention taken in conjunction with the accompanying drawings, the
description of which follows.
FIG. 1 is a block diagram of a printing device utilizing an ink jet
head and having the analyzing system of this invention incorporated
therein.
FIG. 2 is a block diagram illustrating the analyzing system of this
invention.
FIG. 3 is a flow diagram illustrating operation of the
microprocessor shown in FIG. 2.
FIG. 4 shows three examples of start-up pressure waveforms analyzed
by this invention.
FIG. 5 is a diagnostic table.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings, FIG. 1 indicates, in block form, a
printing device 7 having an ink jet head 9 incorporated therein.
Printing devices incorporating an ink jet head are known in the
prior art and this description is therefore limited to the portions
thereof used in conjunction with the analyzing system and method of
this invention.
As shown in FIG. 1, ink jet head 9 is connected with a pressurized
ink supply 11 through valve 13. Although the ink supply is shown to
be pressurized, a separate pressure source could be utilized, it
being only necessary that a pressure build-up be caused to occur in
the ink jet head, in the presence of ink therein, so that the ink
is ejected from the ink jet head to material 15 (commonly paper) to
be inked at an ink application area, as is common for printing
devices utilizing ink jet heads.
Valve 13 is preferably an electro-magneticly actuated valve
controlled by a valve control unit 17 through a valve driver 19. As
is well known, such a valve may be opened by an energizing
electrical output signal from the valve control unit applied
through the driver (or amplifier) 19 to the valve unit. As
indicated in FIG. 1, the electrical output signal from valve
control unit 17 is also coupled to sensing system 21.
As also indicated in FIG. 1, ink jet head 9 has a pressure
responsive transducer 23 to sense the pressure build-up within the
ink jet head. Transducer 23 is preferably a piezoelectric crystal
and is preferably the same crystal that is used to excite the ink
jet head to break the ink stream into droplets.
The output from piezoelectric crystal 23 is an electrical signal
that is proportional to the transient ink pressure against crystal
23 within the ink jet head. This signal is coupled to sensing
system 21 of this invention.
At sensing system 21, the amount of time required for pressure to
build-up to predetermined levels is determined and outputs
indicative thereof are coupled to microcomputer 25 for analysis of
operation of the ink jet head (along with the valve mechanism
associated therewith).
The time between initiation of start-up (by providing an output
signal from valve control unit 17) and the actual start of pressure
build-up in the ink jet head indicates the general condition of the
valve mechanism. If this initiation of start time is out of
tolerance, microcomputer 25 turns on console light 24 to indicate
that the valve mechanism should be checked.
By also determining the amount of time required for the pressure to
build to an operational value, the general condition of the ink jet
head may be determined, as can the likelihood of a clean start of
the ink streams ejected from the ink jet head to the material to be
inked. Depending on the pressure build-up or rise time,
microcomputer 25 will actuate print control 26 to start a print
operation, or to start a self recovery and clean-up procedure for
the ink jet head. Print control 26, which is not a part of this
invention, represents the functions necessary to print including
control of relative motion between the ink jet head and the print
material, data synchronization and deflection of ink droplets, and
self-recovery operations for the ink jet head assembly 9.
FIG. 2 illustrates, in block form, an implementation of the sensing
system 21 of this invention. As shown, gate 29 receives the
electrical signal from valve control unit 17 as one input thereto.
Gate 29 also receives a second input from clock 31 at any available
clock frequency (for example, at a frequency of 16 MHz).
When a signal is coupled from valve control unit 17 to energize
valve 13 to "open" the valve, the signal is also coupled to gate 29
to gate the clock signal therethrough. The output from gate 29 is
connected to delay counter 33 and when an output is provided by
gate 29, this causes delay counter 33 to start to count at a rate
controlled by the frequency of the clock input to gate 29.
As ink passes through valve 13 to ink jet head 9, the pressure in
the ink jet head begins to rise. The increase in pressure in the
ink jet head causes deformation of piezoelectric crystal 23 and
this produces a transient electrical output signal (which may be
amplified) from the crystal that has a pulse height proportional to
pressure. Crystal 23 has a frequency response sufficient to be
sensitive to the pressure rise times to be sensed. Examples of rise
times to be sensed are described hereinafter in reference to FIGS.
3, 4 and 5. Alternatively, a DC pressure transducer separate from
piezoelectric crystal 23 might be placed in the ink jet cavity of
head 9 to supply the pressure signals for the sensing system
21.
Since piezoelectric crystal 23 is preferably also the excitation
crystal for drop generation in the ink jet head, crystal 23, as
shown in FIG. 2, is connected to switch 35 for switching the
crystal between the two different modes of operation (i.e.,
excitation of the crystal by means of crystal drive unit 37 and
sensing of pressure build-up within the ink jet head) by an
external mode control input signal controlling the switch.
When switch 35 is in the sensing mode (as indicated in FIG. 2),
crystal 23 is connected with comparators 39 and 41 of the sensing
system 21 to produce one input thereto. This input to the
comparators indicates the amount of pressure build-up in the ink
jet head.
Comparator 39 receives, as a second input, a reference signal, or
voltage, just sufficient to indicate the start of rise of pressure
within the ink jet head. When the pressure starts to rise in the
ink jet head, the signal coupled to comparator 39 from
piezoelectric crystal 23 increases. When the level exceeds the
reference level, an output is provided at comparator 39, and this
output is coupled to delay counter 33 to terminate the count
thereat (the count having been started at initiation of start-up by
the signal from valve control unit 17 enabling gate 29).
The output signal from comparator 39 is also coupled to gate 43 as
one input thereto. Gate 43 receives, as a second input thereto, the
clock signal from clock 31 so that when an output is received from
comparator 39 (indicating the start of rise of pressure within the
ink jet head), the clock signal is gated through gate 43 to rise
time counter 45 to cause counter 45 to start to count at a rate
determined by the frequency of the clock.
Piezoelectric crystal 23 is also connected to comparator 41 to
couple an input thereto indicative of the pressure within the ink
jet head. Comparator 41 also receives, as a second input, a second
reference level signal, or voltage. This second reference level is
greater than the first level coupled to comparator 39 and is
selected to be indicative of a level within the ink jet head of
almost the supply, or operational, level. When the pressure level
within the ink jet head exceeds the second reference level, an
output is produced by comparator 41, and this output is coupled to
rise time counter 45 to terminate the count thereat.
As also shown in FIG. 2, the count on delay counter 33 is coupled
through logic gate 49 and data bus 51 to delay register 53 of
memory 55 in microcomputer 25, which microcomputer also includes a
microprocessor 57. This count is stored in delay register 53 and
then used to calculate the time delay, or lapse, between switching
of valve control unit 17 and the start of pressure rise in the ink
jet head.
In like manner, the count on rise time counter 45 is coupled
through logic gate 59 and data bus 51 to rise time register 61 in
memory 55 of microcomputer 25. This count represents the rate of
pulse rise, i.e., rise time of pressure within the ink jet
head.
As shown in FIG. 2, the transfer of the counts from counters 33 and
45 is controlled by address decode unit 63. When microprocessor 57
generates the address for delay register 53, address decode unit 63
generates an enable signal for logic gate 49. When microprocessor
57 generates the address for rise time register 61, address decode
unit 63 generates an enable signal for logic gate 59. Gates 49 and
59 transfer the delay count and rise time count to registers 53 and
61, respectively, when enabled.
After transfer of the count on counters 33 and 45 to the memory
registers of microcomputer 25, the necessary calculations,
decisions and records are made utilizing this data. The count data
can be used, for example, to update statistics in the
microprocessor diagnostic logs concerning frequency of valve starts
exhibiting similar counts to thereby generate a frequency
distribution of start speeds. The data, used in conjunction with
microprocessor generated statistics on the trend of machine valves,
can also indicate impending head-valve failures and is therefore
useful in machine maintenance.
FIG. 3 is a flow diagram illustrating operation of microprocessor
57. As shown, it is first determined if the data from delay
register 53 is equal to or greater than a value X.sub.1 (which is
the characteristic valve pick time lower limit and may be, for
example, 3 ms). If not, an output is produced to energize an
indication (such as console light 24-FIG. 1) to indicate a need for
valve maintenance. At the same time, the valve pick number and
delay can be stored in the memory 55.
If the data for delay register 53 is greater than the value
X.sub.1, and is also greater than, or equal to, the value X.sub.2
(which is the characteristic valve pick time upper limit and may
be, for example, 5 ms), then the indication (i.e., light 24) is
energized to indicate the need for valve maintenance in the same
manner as if the value was less than the value X.sub.1.
If the data for register 53 is greater than, or equal to, the value
X.sub.1, but is less than the value X.sub.2, then the data is
obtained from time rise register 61. Also, if valve maintenance has
been indicated, the microprocessor still obtains the rise time
data. If the rise time is within limits, the printing operation can
proceed even though the valve operation is out of tolerance.
The frequency distribution of the rise time is next updated. If the
rise time is greater than, or equal to, a value X.sub.3 (which is
the rise time upper limit and may be, for example, 5 ms), then the
machine is instructed to initiate a self-recovery procedure, after
which the start procedure is automatically repeated.
If the rise time is less than the value X.sub.3, and is less than a
value X.sub.4 (for example, 2 ms), then the machine is instructed
to supply ink to the material and thus to start the print
operation.
If the rise time should be greater than, or equal to, the value
X.sub.4, and less than the value X.sub.3 (indicating that there is
some air in the head), the machine is delayed by a value Z (which
is the delay time required to dissolve unwanted air from the ink in
the ink jet head), after which the machine starts to print.
Referring now to FIG. 4, three examples of the rising edge of the
pulse from crystal 23 are shown. The start times t.sub.1 and the
rise times t.sub.2 are identified for each wave form by the
subscripts A, B, and C for waveforms A, B, and C, respectively.
Waveform A represents a normal start-up where the valve operated
within tolerances and the pressure rise time t.sub.2A indicates a
proper start-up of the ink jet.
Waveform B is an example where valve actuation was within tolerance
but the pressure build-up is too slow. The likely result of the
slow pressure build-up is that ink is sprayed onto the other
components in the ink jet head assembly. It is very likely that a
successful print operation could not occur and therefore, a
recovery procedure would be initiated.
Waveform C is an example where the start time indicates that valve
actuation is out of tolerance, however, once started the pressure
rise time build-up is normal. In this situation, a normal print
operation could be expected but the valve would be marked for
maintenance in anticipation of a future failure.
The diagnostic table in FIG. 5 shows the criteria for selecting the
values X.sub.1, X.sub.2, X.sub.3, and X.sub.4 used by the
microprocessor 57 as described in the flow diagram of FIG. 3.
When the start time is less than X.sub.1, or greater than or equal
to X.sub.2, the valve is out of tolerance and a failure of the
valve in the future can be expected. A rise time of less than
X.sub.1 might be caused by the valve being out of adjustment or the
valve actuation being too short in its stroke in turning ink flow
on and off.
The start time being greater than or equal to X.sub.2 can be an
indication that the valve mechanism is slow, possibly because it is
dirty. It can also indicate that the electronic drive for the valve
solenoid is weak or possibly the solenoid itself is weak. Waveform
C in FIG. 4 is an example of the start time being greater than
X.sub.2.
The rise time t.sub.2 being greater than or equal to X.sub.3 is an
indication that the pressure build-up was too slow. In this
situation, it is highly probable that the ink jet head assembly
will be wetted by the ink jet. This might be caused by excessive
air in the ink cavity of the head or by a failure in the pressure
system pressurizing the ink. Waveform B in FIG. 4 is an example of
a rise time greater than X.sub.3. The rise time being greater or
equal to X.sub.4, but less than X.sub.3 is an indication that the
ink pressure build-up in the head was slow but probably not so slow
as to cause a wetting of the head assembly during start-up. This
may indicate that the ink jet stream would be hard to control but a
printing operation can likely proceed successfully. One probable
cause for the slower than normal rise time is air in the head. By
allowing a period of delay before the print operation begins this
air can usually be removed by being dissolved into the ink. Of
course another source for the slow rise time might be a low ink
pressure. In this case the ink stream may be hard to control.
If the rise time t.sub.2 is less than X.sub.4 the pressure build-up
in the head is normal and a good printing operation can be
expected. Waveforms A and C are examples of proper rise times.
While some start times and rise times have been earlier given as
examples, it will be appreciated by one skilled in the art that an
acceptable rise time and an acceptable start time will depend on
the ink jet printing system. Values of X.sub.1, X.sub.2, X.sub.3,
and X.sub.4 may be selected and easily changed by reprogramming the
microprocessor. The values used will depend upon the ink jet
assembly which the invention system is monitoring.
Thus, a high count on register 53 can be used to indicate the need
for valve maintenance, while a high count on register 61 can leave
the machine in a "not ready" mode to dissolve entrapped air and
thus insure proper drop generating action. The value of the high
counts can also be used to initiate discreet levels of machine
self-recovery, such as air purging of the head, valve starting
re-tries, or deflection electrode cleaning.
While not specifically shown, it is also to be appreciated that the
system and method could also be utilized to time the speed of
pressure decay in the ink jet head at valve shut-off in the same
manner as described hereinabove with respect to start-up. Such
information can, of course, also be utilized to determine proper
operation of the ink jet head and associated valve mechanisms.
As can be appreciated from the foregoing, this invention provides a
system and method for automated dynamic analysis of a device such
as an ink jet head and can, by way of example, detect a sticking
valve, air ingestion during valve cycling, incomplete air purging
after head replacement, and/or air leaks in the ink system.
While we have illustrated and described the preferred embodiment of
our invention, it is to be understood that we do not limit
ourselves to the precise constructions herein disclosed and the
right is reserved to all changes and modifications coming within
the scope of the invention as defined in the appended claims.
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